Neural tube defects (NTD), the most frequent and severe central nervous system malformations, are a major cause of perinatal death and lead to life-long handicap in survivors. For several years, we have studied the curly tail mouse mutant because of its similarities in inheritance, associated abnormalities, and type and morphology of neural tube lesions to NTD in humans. Our prior work has shown that curly tail mice produce NTDs in a consistent and reliable manner, that a mutation at a single locus, (ct), produces the lesion, that the penetrance of this recessive Mendelian trait is affected by modifier genes, and that our curly tail stock is genetically homogeneous with respect to these genes. Our initial gene mapping indicates provisional linkage of the ct locus to the distal region of Chromosome 4. Moreover, our finding that the NTD can develop in whole embryo culture has led to our defining the site and time of onset of the morphogenetic defect closure of the posterior neuropore, apparently due to an enhanced ventral curvature resulting from an imbalance in cell proliferation in tissues of the posterior neuropore region. The NTD is associated with an abnormally low rate of accumulation of basement membrane hyaluronan beneath the neurepithelium at the site and time of neuropore closure. However, transferrin, a growth factor, also appears in association with posterior neuropore closure. These results lead to our overall hypothesis that the ct locus encodes a protein involved in controlling cell proliferation in embryonic axial tissues at the time of neurulation. Our specific aims are to: (i) confirm the chromosome assignment and create a high-resolution genetic map around the ct locus using polymorphic DNA markers and backcrosses of curly tail with Mus spretus mice, (ii) isolate DNA fragments containing the ct locus using mouse YAC (yeast artificial chromosome) libraries and identify candidate genes from conserved regions and by analyzing appropriate expression patterns in the embryo, (iii) produce a congenic strain of curly tail mice to enable the screening of curly tail embryos for abnormalities in gene products, (iv) identify the embryonic tissue in which the ct defect is primarily expressed by construction of chimeric embryos containing cells of curly tail and wild type origin. (v) Evaluate the pathogenetic role in curly tail NTD of transferrin, hyaluronan and retinoic acid, each implicated in neurulation by experiments involving culture of curly tail embryos.